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The comments by Gen. David Petraeus came on the eve of a rare security summit in which the U.S. will sit down with Syria and Iran.

The White House, however, made clear Thursday it won't necessarily be a friendly chat with the Iranians: U.S. negotiators plan to warn Iran to stop funding, supplying and training Iraqi militants.

"It is time for them to knock this off and play a constructive role," national security adviser Steve Hadley said en route to Latin America with President Bush.

"This is not about engaging Iran and Syria. It is about getting the countries of the region and the broader international community to support Iraq," he said.

Petraeus, meanwhile, held his first press conference since taking command as delegates prepared for the gathering in Baghdad to try to find a way to halt violence between Sunnis and Shiites.

"Military action is necessary to help improve security . . . but it is not sufficient," Petraeus said.

The general said political talks must eventually include some militant groups now opposing the U.S.-backed government.

"That is what will determine in the long run the success of this effort," Petraeus said.

Top diplomats, meanwhile, hope the presence of Iranian and Syrian delegates at the security summit will create a de facto truce in the world's most dangerous capital. A massive troop presence is routine in Baghdad, but that has been unable to halt the daily suicide bombers, car bombs and snipers that have turned much of Baghdad into a no man's land.

"It will be the safest place in Baghdad, we have no doubt," said a European diplomat, who hoped for an unofficial ceasefire while talks are under way.

Syria, Iran, Turkey, Jordan, Saudi Arabia, Kuwait, Egypt, the five permanent Security Council members - U.S., Britain, China, France and Russia - the Arab League and the Organization of the Islamic Conference have been invited.

The envoys are expected to meet in the heavily fortified Green Zone, where the Iraqi government and U.S. leaders are headquartered. But a U.S. counterterrorism official said there's no way to be 100 percent safe even in that secure area.

"As any New Yorker knows, you're not safe anywhere, but you still have to go to the meeting," the official said.